From the past, a microstrip antenna is known in which an antenna electrode and a ground electrode are respectively disposed upon the front surface and the rear surface of a substrate, and which generates radio waves from an antenna electrode in a perpendicular direction by applying a high-frequency microwave signal between the antenna electrode and the ground electrode. The following types of techniques are known for controlling the radiating direction of the synthesized radio beam which is generated from a microstrip antenna. For example, with the technique described in Japanese Laid-Open Patent Publication Heisei 7-128435, a plurality of antenna electrodes are disposed upon the surface of a substrate, and the radiating direction of the synthesized radio beam is changed by switching a high-frequency switch, thus changing the lengths of the electrical supply lines for the high-frequency signal to the antenna electrodes. In other words, by the lengths of the electrical supply lines to the plurality of antenna electrodes being different, a phase difference is created between the radio waves which are respectively generated from each of the plurality of antenna electrodes, and the radiating direction of the combined and synthesized radio beam is inclined towards that antenna whose phase has been delayed. Furthermore, for example, with the technique described in Japanese Laid-Open Patent Publication Heisei 9-214238, a plurality of antenna electrodes are provided whose radiating directions for synthesized radio beams are different, and the radiating direction of the synthesized radio beam is changed by switching the antenna electrodes to which a high-frequency signal is applied with a high-frequency switch. Furthermore, in Japanese Laid-Open Patent Publication 2003-142919, there is described a multibeam antenna of a feed point changeover type which includes a plurality of feed elements and a plurality of parasitic elements upon the surface of a substrate. With this multibeam antenna, it is arranged to be possible to connect or disconnect all or a portion of the plurality of feed elements to a feed terminal via switches. And it is arranged to be possible to select the radio beams whose radiating directions are different by switching the feed elements feeding by the switches.
A body detection device is known which uses radio waves generated from a microstrip antenna. With this body detection device, by varying the radiating direction of the synthesized radio beam which is emitted from the microstrip antenna as described above, it becomes possible to detect the position and the situation of a body more accurately, as compared to the case in which the radiating direction of the synthesized radio beam is fixed. For example, by scanning the radiating direction of the synthesized radio beam which is transmitted from the microstrip antenna over a two dimensional range by varying its X and Y directions, it is possible to ascertain the presence or absence of a body, and the situation thereof, over a two dimensional range. There are many applications for such a body detection device, such as, for example, target detection for an automatic tracking missile, or user detection for a toilet device, or the like. In whichever application, it is extremely useful to be able to vary the radiating direction of the synthesized radio beam which is transmitted from the microstrip antenna. For example, to focus the discussion upon the case of a user detection device for a toilet device, if the position or the state of a user is detected more accurately, then it is possible to control a washing device or a deodorization device or the like of a toilet in a more appropriate manner. Now, simply from the objective of ascertaining the state of the user accurately, perhaps it would be preferable to utilize a camera, but it is naturally impossible to use a camera for a toilet device. Accordingly, with a body detection device which employs radio waves, it is extremely important to make it possible to ascertain the state of the user more accurately by controlling the radiating direction of the synthesized radio beam. In this connection, in Japan, it is possible to utilize the frequencies of 10.525 GHz or 24.15 GHz with the objective of detecting a human body, and to utilize the frequency of 76 GHz with the objective of onboard collision prevention.